Osteoarthritis prevalence and modifiable factors

The prevalence of hand, knee, or hip joint OA has increased from 21 million in 1995 to an estimated 27 million among adults in the United States. Such increases are likely due to aging of the population and the rising prevalence of obesity.

Osteoarthritis (OA) is the most common articular disease of the developed world and a leading cause of chronic disability, mostly as a consequence of knee OA and/or hip OA. The economic costs of OA are high, including those related to treatment, for individuals and their families who must adapt their lives to the disease, and those due to lost work productivity. The prevalence of hand, knee, or hip joint OA has increased from 21 million in 1995 to an estimated 27 million among United States (US) adults. Such increases are likely due to aging of the population and the rising prevalence of obesity.

OA has a multi-factorial etiology, with different sets of factors associated with its incidence. Factors associated with OA have been broadly divided into person-level factors and joint-level factors. Person-level factors include age, sex, obesity, genetics, race/ethnicity and diet. Joint-level factors refer to factors that are unique to a particular joint such as injury, activity, type of occupation, and muscle strength. Factors associated with OA have also been classified as those that relate to OA development and those relating to disease progression. In terms of knee OA, Doherty, reports factors such as age, sex, occupation, weight status and recreational activity can play a role in the development of OA, and weight status and dietary factors may play a role in its progression.

When considering non-modifiable factors for OA, age and sex are the strongest predictors. For example, women are at greater risk for developing knee and hip OA compared to their male counterparts. Hormonal factors,reduced volume of cartilage in the knee, and the fact that women are more likely to self-report have been considered as explanatory factors.

Obesity is a strong modifiable risk factor for the development of knee OA, but less so for hip OA. In a meta-analysis, those who were obese or overweight were nearly three times as likely to report knee OA. The effects of obesity on OA are through both mechanical and systemic mechanisms. Obesity can exert an increased load as a consequence of increased body weight, however there may be differential systemic effects depending on the degree of fat versus lean mass, involving the activity of adipocytokines.

Other modifiable factors of OA include occupation, dietary factors and physical activity. For example, repetitive joint loading through kneeling or squatting have been shown to be associated with an increased risk of knee OA, and this risk is even greater for those who are overweight. Furthermore, occupational lifting and prolonged standing have also been most strongly associated with hip OA.

A number of studies have examined the role of vitamins (such as vitamins D and C) in OA. Mechanistically, it is thought that vitamin C may serve to decrease cartilage loss in the joints while low vitamin D intake and reduced circulating serum vitamin D may confer an increased risk of knee OA.

The benefits of physical activity for OA are well-established, with national service organizations promoting active lifestyles, including walking for individuals with OA. However, most individuals with knee OA do not meet recommended physical activity guidelines. Findings from a recent study has reported most people with knee OA are capable of walking at the recommended intensity needed to meet physical activity guidelines, and their knee pain has little impact on their level of physical activity.

Factors associated with OA could also interact in complex ways. For example, healthy lifestyle behaviours may reduce the age-related onset of OA, and there can also be additional multifaceted associations between factors associated with OA. Considering the rising prevalence of OA in the population, identifying modifiable factors associated with OA is important to guide the development of effective interventions. Currently, there appears to be a paucity of data, particularly for Canada.

Using a large population sample consisting of random community samples, the objectives of this study were to:

investigate the prevalence of self-reported knee and hip OA stratified by age and sex; and,